The present invention relates to a gas sensor installed in an exhaust system of an internal combustion engine to control the combustion of this engine.
A conventional gas sensor used for controlling the combustion of an internal combustion comprises a cylindrical housing, a gas sensing element disposed in this housing, an atmospheric side cover provided at a proximal end of the housing, and a measured gas side cover provided at a distal end of the housing.
A front end (i.e., distal end) of the gas sensing element is accommodated in the measured gas side cover and is exposed to the measured gas. A proximal end of the gas sensing element is closed by the atmospheric side cover. Output terminals of the gas sensing element extend out of the gas sensor from the proximal end side.
A sealing member, an insulator, a packing or the like are provided in an annular clearance between the gas sensing element and the housing to airtightly close the clearance.
In other words, the sealing members provided between the gas sensing element and the housing serve as a partition for separating an air atmosphere in the atmospheric side cover from a measured gas atmosphere in the measured gas side cover. If the measured gas leaks into the air atmosphere from the measured gas atmosphere, the measuring accuracy of gas concentration will deteriorate. It is thus desirable to maintain high airtightness between the gas sensing element and the housing.
However, the measured gas may contain gasoline or other liquefied component. Due to its liquid nature, the gasoline or other liquefied component has the capability of smoothly penetrating into the sealing members (more specifically, micro holes and clearances residing in these sealing members). Thus, the gasoline (in the form of liquid or gas) possibly leaks into the air atmosphere. Such leakage of gasoline or other liquefied component deteriorates the accuracy in the measurement of gas concentration, too.